Under recent increase of waste paper recovery rate, low-quality waste paper is also recycled as raw materials for paper making. For that reason, the amount of pitch introduced into paper-making system is increasing year by year in papermaking step. Proposed as the conventional methods for suppressing flocculation of pitch and deposition thereof on apparatuses in the papermaking step were methods of using polyvinyl alcohol (see, for example, Patent Documents 1 and 2).
It is considered that polyvinyl alcohol, which has hydrophobic and hydrophilic groups, prevents deposition of pitch on wire, because the hydrophobic groups bind to the pitch hydrophobically and the hydrophilic groups disperse the pitch. Thus in the case of conventional pitch control agents, the block nature of the hydrophobic groups and the saponification index of polyvinyl alcohols were studied.